Known electrically operated fuel injectors which impart a swirling component of motion to the fuel being injected place the largest portion of the pressure drop across the swirl-inducing device. Such fuel injectors either retain a relatively large volume of "dead" or non-swirl fuel below the swirl-inducing device or else place the swirl-inducing device downstream of the valve seat where the possibility of objectionable post-injection drip may exist. In either case, the quality of the injection may be compromised by the introduction of a certain amount of non-swirl fuel into the combustion chamber. Accordingly, there is room for further improvement in enhancing the swirling character of an injected fuel cloud.
In order for a spark-ignited internal combustion engine to exhibit acceptable part throttle (part load) operation, it has been found important that a fuel injector create a finely atomized cloud of fuel that is distributed over a large extent of the combustion chamber volume close to, but preferably not colliding with, the combustion chamber walls.
The present invention is directed toward a novel fuel injector that operates to enhance the swirling character of the injected fuel cloud. It has been discovered that the invention can create an injected fuel cloud which possesses a distinctly toroidal shape. Such discovery has been made and measured through the use of sophisticated photo-optical techniques including stroboscopic photography, helium-neon laser beam diffraction, and principles including Fraunhofer diffraction. As engine speed increases, it is desirable that the injected fuel cloud become increasingly spaced from the combustion chamber wall. By having a small dead-volume, a fuel injector according to the present invention is especially suitable for high-speed operation such as that which can occur in a two-stroke engine, and in such case, the fuel injector is supplied with fuel which is pressurized to a pressure that is considerably higher than that customarily used in today's fuel injection systems for four-stroke engines. Additionally, the invention is capable of producing a relatively circumferentially uniform swirl in the injected fuel from a limited number of circumferentially separated swirl passages in the swirl inducing device.